Session value is not passing

In my page load am getting some request query string value and assigned that to session like this

Session["fname"] = Request.Querystring["name"];

Session["lname"] = Request.Querystring["age"];

Session["email"] = Request.Querystring["email"];

and paypal payment code is

string redirecturl = "";
string amount = Session["dollarrate"].ToString();
// Mention URL to redirect content to paypal site
redirecturl += "https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_xclick&business=" + ConfigurationManager.AppSettings["paypalemail"].ToString();

// First name i assign static based on login details assign this value
redirecturl += "&first_name=name";

// City i assign static based on login user detail you change this value
redirecturl += "&city=city";

// State i assign static based on login user detail you change this value
redirecturl += "&state=city";

// Product Name
redirecturl += "&item_name=Property Verification Charge";

// Product Amount
redirecturl += "&amount=" + amount;

// Business contact id
redirecturl += "&business=email";

//Shipping charges if any
redirecturl += "&shipping=5";

// Handling charges if any
redirecturl += "&handling=5";

// Tax amount if any
redirecturl += "&tax=5";

// Add quatity i added one only statically
redirecturl += "&quantity=1";

//Currency code
redirecturl += "¤cy=USD";

//Success return page url
redirecturl += "&return=ConfigurationManager.AppSettings["SuccessURL"].ToString();

// Failed return page url
redirecturl += "&cancel_return=" + ConfigurationManager.AppSettings["FailedURL"].ToString();
Response.Redirect(redirecturl);

after click and payment is properly finished but the paypal page is redirected success page am not get the session value. it all is going to null. but this code is working properly in local server but not in online server...